The invention relates to the technique of recording and re-producing spatial sound. As home theatres are becoming more common, a large portion of consumers has a home theatre. The aim of home theatres is to reproduce credible spatial sound, such as in a recording situation. At present, the equipment is most generally of type 5.1, including two front loudspeakers, a central loudspeaker, two back loudspeakers and one subwoofer controlled by the LFE channel for low-frequency sound effects. Other such Surround systems include the 7.1, 8.1 and 10.2 systems, for example, part of which are designed only for theatre use, not for an ordinary consumer. However, such 5.1 equipment requires six channels and does not include elevation information. In such systems, the loudspeakers are to be placed at the designed locations around the listener.
However, it is practically impossible to reproduce sound according to the original recording situation, and consequently, techniques have to be employed for producing a sound world that sounds as authentic as possible. For example, in reproduction with earphones, attempts have been made to model the behaviour of the ear with HRTF (Head Related Transfer Function). However, a signal modified with HRTF has conventionally been an artificially panned mono source.
In the 1970's, a technique called Ambisonics, which was designed as a recording technique for spatial sound, was developed for recording and reproducing spatial sound. However, in recording sound, the Ambisonics technique is expensive. In recording, a Soundfield microphone has to be employed that tends to receive the entire 360° sound field by means of four adjacent cardioid capsules placed in the form of a tetrahedron. Patent publication EP 0869967 B1 discloses a microphone intended for recording spatial sound. Therein, the microphones have an omni-directional pattern. In this case, the microphones have to be placed on the surface of a hard ball. Between the several microphones placed on the surface of the ball is a distance of the length of the diameter of the ball. This distance causes harmful time differences.